US3434770A - Reduction of arcing between the parts of a cathode ray tube - Google Patents

Description

March 25, 1969 G, V. ANGELUCQ ET AL. 3,434,770

REDUCTION OF ARCING BETWEEN THE PARTS OF CATHODE RAY TUBE 4 Filed May 19, 1967 FIGI HIGH VOLTAGE TRANSFORMER TIMER NO2 FIGZ RlcHARD J. KURTZ RICHARD s. o'FALLoN BY QMQMMW ATTORNEYS I 4 .T 6 S l. e e C 4./.T S C VT 9 .l Dn U No m O L CC T E N G E N e IM VA g N C 7 I V n z/rdm E WWS eo G @A OW R m A m G e r d 2 A r u mw C mm GF A 2 7 2 O 4 7 IL I, I 5 Ian/ w1 MI nld, HI kn g .m 11:. IIIM f I u. w u \\w \m 4 O wav 3 3 l United States Patent O U.S. Cl. 316--1 9 Claims ABSTRACT OF THE DISCLOSURE High voltage aging of a cathode ray tube to neutralize arcing is accomplished by placing a grounded metal band about the neck of the tube. The band establishes a ground plane about the neck in which electrical elds are developed which simulate the iields developed during normal tube operation in a tele-vision receiver. A high aging potential is applied between the final anode and the grids of the electron gun assembly, which are grounded, in stages from between 15,000 volts to 40,000 volts. During each stage the voltage is periodically boosted from 5,000 to 10,000 volts over the stage voltage, for a predetermined time, to foster arcing between the tube parts.

Cross-reference to related application Patent No. 3,321,263, issued May 23, 1967, and assigned to the assignee of this application, describes a process for reducing arcing in a cathode ray tube.

Background of the invention Although the pieces of an electron gun assembly can be cleaned chemically, there still remains trace impurities on the guns which are capable of undesired emission of electrons, Satisfactory processes have been developed for the reduction of arcing between the parts of the cathode ray tube in a color television receiver in which the electron gun structure includes a final anode operating at a potential on the order of 25,000 volts, and focus, screen and control grids operating at a potential from between 5,000 volts for the focus grid to 130 volts for the control grid. Because of the potential difierence between the nal anode and the dilierent grids, this undesired emission of electrons can foster arcing between the different gun parts, which is annoying to the viewer and harmful to the gun assembly. Generally, the practice in the past has been to hit the anode of the tube with a high potential with the grids grounded to arc out the tube to burn otf the trace impurities from the gun. This arcing out is followed by high voltage aging at a potential of around 40,000 volts for time in excess of 1 hour. The time required for the high voltage aging necessarily adds to the production time required to make a tube.

Electron gun assemblies have been developed for cathode ray tubes used in color television receivers, which are based upon a Zero focus principle. That is, the focus grid is coupled to a reference potential and is positioned intermediate first and second accelerating electrodes which are electrically connected to one another by a shield which is positioned about the focus electrode. A potential on the order of 25,000 volts is coupled to the two accelerating electrodes. This brings the high voltage much further down into the neck of the tube as cornpared to the conventional tri-beam electron gun assembly thereby increasing the arcing problem between the tube parts.

Summary It is an object of this invention to provide the method and associated apparatus necessary for carrying out a high voltage aging process which reduces the production time required to make a cathode ray tube.

It is another object of this invention to provide the method and necessary apparatus for carrying out high voltage aging in a color television tube that reduces the` tendency for arcing between the parts of the electron gun assembly when a high potential exists deep in the tube neck.

In practicing one embodiment of this invention, a tribeam electron gun assembly is mounted in the neck of a cathode ray tube used in a color television receiver. Each gun includes a focus electrode connected to a reference potential and positioned intermediate rst and second accelerating electrodes, which are connected to each other by a shield positioned about the focus electrode. The accelerating electrodes are connected to a potential in eX- cess of 25,000 volts while the focus electrode is operated at ground or at a relatively low reference potential. The screen and control grids, which are also operated at a relatively low potential, are coupled along with the focus grid to stem connectors supported in the tube stem. The gun electrodes are subject to contamination by trace impurities which are capable of undesired emission of electrons. The high voltage aging process of this invention utilizes arcing to burn off these impurities, and high voltage aging to neutralize the impurities to reduce the possibility of arcing during the tube life. During the process, the tube stem connectors are grounded, grounding the focus, control and screen grids. A metal strap is positioned about the tube neck and grounded. This metal strap establishes a ground about the tube neck which simulates the ground plane formed about the neck of the cathode ray tube during normal operation in a color television receiver, by such devices as the convergence and deflection yokes. A high voltage on the order of 15,000 volts is applied to the accelerating grids for a predetermined time. This voltage is increased briefly to 25,000 volts every few seconds to foster arcing of the tube. After the predetermined time, the voltage is increased to 25,000 volts and is periodically boosted to 30,000 volts. The aging potential is thus increased in stages until the base voltage is 40,000 volts, which is periodically boosted to 45,000 volts, At the end of the process, the trace impurities are burned od or are neutralized so that under normal tube operating voltages there will be little chance of arcing between the parts of the electron gun assembly.

In the drawings:

FIG. 1 is a schematic showing of the apparatus used in the process of this invention;

FIG. 2 is a cross-section view of the neck portion of a cathode ray tube in accordance with this invention; and

FIG. 3 is a block diagram illustrating the steps of the process in accordance with this invention.

Detailed description Referring to the figures of the drawing, FIG. 1 shows a color cathode ray tube 10 which has a glass necked envelope 12, containing an electron gun assembly (FIG. 2) for producing three electron beams. The inside of the funnel portion 14 has an Aquadag (trademark of Achesorl Colloids Company `for their brand of colloidal graphite in water) coating 16 extending a short distance along the inside surface of the neck envelope 12. The coating is electrically connected to a portion of the electron gun assembly. A face panel 18 is connected to the funnel portion 14 and includes a shadow mask structure 20 and a viewing screen 22 consisting of phosphor dots which'emit colored light when impinged by an electron beam. The

viewing screen 22 is composed of triads of phosphor dots, with the apertures of the shadow mask structure restricting the beams to associated ones of the dots and triads for reproducing a colored image.

FIG. 2 illustrates in detail the electron gun assembly within the neck portion 12 of the tube 10. The electron gun assembly includes three electron guns one of which is shown in detail at 25. In this view, only a small portion 26 and 27 can be seen of the other two electron guns of the assembly. In the electron gun assembly 25, an electron beam is generated by a cathode (not shown), which is processed and accelerated by the control electrode 30, a screen electrode 34 and rst and second accelerating electrodes 36 and 33. Positioned intermediate the accelerating electrodes is the focus electrode 4t). A slightly curved shield 42 provides electrical connection between the accelerating electrodes 36 and 38 and reduces exposure of these electrodes and the focus electrode to the glass neck of the television tube. A convergence assembly 45 is connected to the accelerating electrode 38 and completes the electron gun assembly. The assembly 45 has a number of contacts 47 connected thereto which electrically connect the assembly 45 to the inner Aquadag coating 16. The convergence assembly 45 converges three beams from the electron gun into a single beam which is deected by the deflection yoke (not shown) mounted to the shadow mask assembly in the known manner.

In order to provide convenient points for connecting the cathode ray tube to circuitry in a television receiver, the cathode, control electrode 30, screen electrode 34 and focus electrode 4t) are attached to stem connectors 48, which are mounted exteriorly of the neck envelope 12 in the stem piece 50. In addition, the Aquadag coating 16 is attached to a terminal 52 (FIG. 1) mounted exteriorly of the funnel portion 14 for connection to the receivers high voltage signal. The order of magnitude of the voltages which may exist at the connectors 48 and the terminal 52 are as follows. A direct current potential on the order of kilovolts is applied to terminal 52 to establish the Aquadag coating 16, the convergence assembly 45, and the first and second accelerating electrodes 36 and 38 for each gun assembly at this 25 kv. potential. The focus electrode is connected through connector 4S to ground reference potential, or to a potential which is relatively much lower than the potential on the first and second accelerating electrodes, for instance, 1 kv. The screen electrode 34 may be at 45() volts, the control electrode 32 at -20 volts and the cathode electrode at 20() volts.

By connecting the focus electrode 40 at or near ground potential, shielding the gaps between the first and second accelerating electrodes 36 and 38 and the focus electrode 40 greatly reduces the possibility of electric elds within the tube neck causing convergence drift of the electron beam that passes through the focus electrode 40 so that little or no focusing of the electron beam during reception of a transmitted signal will be necessary. This type of electron gun assembly is commonly referred to as operating on the zero focus principle.

Electrically connecting the first and second accelerating electrodes 36 and 38, however, brings the high voltage potential of approximately 25 kv. down much further into the neck 12 of the tube than is found in electron gun assemblies for use in color television receivers where only the final anode is maintained at such a high potential. Furthermore, because the faceplate panel 18 is preferably rectangular in conguration when viewed from the front, and the tube has a relatively wide deflection angle of the beam (for example 90 or more), the overall length of the tube may be made as short as possible, and the receiver in which the tube is used may be compact. However, reducing the dimensions of the tube requires placing the electron guns in the assembly much closer together, for instance, in a typical tube the neck portion 12 may be on the order of 11/2 inches in diameter. Due to the high potential differences between the first and second acceleratng electrodes 36 and 3S and the stem connectors 48 a current will flow through the glass envelope to develop a charge thereon. Other factors contributing to the presence of neck charge are cold emission from the electrodes to the neck, imperfections on the surface of the glass, and residue remaining thereon after the glass has been cleaned. Thus there may be arcing between the neck 12 of the tube, which can be at a potential as high as 25,00() kv. or more and one or more of the electrodes 30 and 34. There may also be arcing between the various electrodes themselves because they are at widely different potentials and in closely spaced relation within the tube neck.

Patent No. 3,321,263, issued May 23, 1967, and assigned to the assignee of this application describes a high voltage arc-out and aging process which substantially reduces the possibility of arcing among the gun parts. However, introducing a high potential deeper in the tube neck, as occurs when using a zero focus-type electron gun assembly, has added complications which this invention is especially suitable for curing.

Considering a time after the guns have been chemically cleaned and the tube is assembled with the gun in a tube ncck, which has been acid rinsed, the evacuated and sealed tube undergoes a getter hashing step 60 (FIG. 3). This is a known process involving the activation of a gas absorbing material within the bulb of the tube to reduce the residual quantity of gas remaining after vacuum pumping of the tube.

Following getter flashing, the turbe is ready for step 62, the high voltage aging process of this invention. A braided copper strap is wrapped around the tube neck. The tube is supported in a vertical manner such that the neck portion 12 extends into a container 67 which contains a plurality of fibers of a good conducting material 69, for instance, steel wool. With the tube in this position, the stem connectors 48 extend into the steel wool and make electrical connection therewith. The braided strap 65 has a portion which extends down the side of the tube and into the steel wool. Another portion of the strap 72 extends from the container 67 and is connected to a suitable ground reference potential. With the strap 65 connected to ground, the focus electrode 4G, screen electrode 34 and control electrode 32 are all maintained at a ground potential through the stern connectors 48.

With the tube in this position, a pair of Variacs (trademark ot General Radio Company) 7d and 72 are connected to a high voltage transformer 74. The output o the high voltage transformer' 74 is connected through resistor 75 and coupled 'by lter capacitor 77 to the anode 52 of the tube It). A pair of timing devices 78 and 80 operate respective solenoids 82 and 84 for applying the preselected outputs of Variacs '70 and 72 to the high voltage transformer.

In this aging process, a high voltage is applied to the anode 52 in increasing stages commencing with 15 kv. and ending with 40 kv. During each stage, the aging voltage is periodically boosted from 5 to 10 kv. above the stage voltage to foster arcing between the tube parts. For instance, in a typical first stage, a 15 kv. potential is applied to the anode 52 for a period of 3 minutes. During this three minute period, the 15 kv. potential is alternately applied every 5 seconds, with a 10 kv. booster potential which raises the potential to 25 kv., for 2 seconds to foster arcing. The aging potential will cause the trace impurities on the electron guns to emit electrons as cold emitters, or due to electric field emission. As an example of a trace impurity or contaminant, consider silicon or oxide silicon on the surface of one of the electrodes which would emit electrons under the aging potential- This electron emission will cause ionization of any residual gasses in the tube which have not been absorbed in the getter flashing step 60, and a blue glow may be noted in the region of the neck 12 of the tube. With the residual gasses thus ionized, these ions tend to strike or bombard the emissive contaminants on the surface of the gun electrodes to poison them, or

render them less effective as electron emitters. Accordingly, through each stage of this process, the blue glow gradually diminishes since cold emission is reduced and, therefore, the ionization of the residual gasses is reduced. At the same time, the arcing which is periodically induced in the tube by the addition of the Ibooster potential at each stage tends to burn or melt any of the foreign particles, sharp points, or imperfections on the electron gun assembly to eliminate the gun assembly of the trace impurities which can cause arcing. The resistor 75 is on the order of 60K ohms to limit the current that can pass through the gun parts to insure that they are not damaged during the process. Furthermore, the arcing is only carried out Afor a very short time, i.e., two seconds and then stopped by reducing the potential back to the stage base potential. Therefore, the arcing is prevented from becoming regenerative and possibly burning up the gun parts.

The following table illustrates one schedule that was satisfactorily followed in accordance with the principles of this invention. It is significant that the combined high voltage aging and arc-out process only consumed a total of 35 minutes of time, and the tube subsequently satisfactorily passed a test where a test potential was supplied in steps from 30 kv. to 40 kv. and no arcing was indicated.

In this illustration, Variac 70 could be used for applying the base potential in stages, and Variac 72 could be adjusted to provide the booster potential for each stage. Timers 1 and 2 may be any commercially available timing mechanism which would be operated to alternately energize solenoids 82 and 84 to apply the potential in 5 or 2 second steps as required.

Due to the fact that the high voltage operating potential of the tube is brought down much further in the neck of the tube than with the conventional tri-beam electron gun, it is necessary, in order to get the proper arcing action along the tube neck during the high voltage boost phase of each stage of the process, to place the metal band 65 about the tube neck 12 as shown in FIG. 2. This metal band establishes a ground plane about the tube neck and exterior to it which develops electric fields about the neck when the agingpotential is applied between the gun parts. With this band in place, vicious arcing between the tube parts can be observed, which does an excellent job in burning olf the trace contaminants. An important characteristic of the braided strap is that it forms a ground plane about the neck of the tube and electrical iields thereabout which actually simulate the ground plane and iields established about the neck of the tube by such devices as the convergence and deflection yokes under normal operating conditions in a color television receiver. It was found that without this metal strap encircling the tube, the process was not nearly as effectual in producing the desired result. The strap 65 may be located anywhere along the neck of the tube but it was found that best results were obtained with the strap positioned about the neck of the tube in the vicinity of the convergence assembly 45. Furthermore, the invention is not necessarily limited to the use of a metal strap, as other devices could be used satisfactorily, For instance, a foil of a good conducting material could be completely wrapped about the neck of the tube and extended the length thereof. With this type of application satisfactory results were also obtained.

Referring once again to FIG. 3, after the high voltage aging process the cathode is activated in step 64, by providing a current to the lament of the cathode, considerably in excess to normal operating current, for high heating of the cathode as is known in the art. Activating the cathode takes approximately 30 minutes. In step 90 the cathode is aged at a potential reduced from that necessary to activate the cathode. Cathode aging requires from l to 2 hours. After aging of the cathode, an outer Aquadag coating is added to the tube at step 92, and is followed by step 94, which is a nal test to insure that the tube meets the manufacturers specifications.

What has been described, therefore, is a method and the necessary apparatus for conducting a high voltage arc-out and aging process which reduces the production time for a cathode ray tube, and which greatly reduces the probabilities of arcing between the electron gun parts in a color television tube with the high voltage operating potential brought far down into the neck of the tube.

We claim:

1. A process for reducing the tendency of arcing among the parts of a cathode ray tube having an electron gun structure positioned in the tube neck which includes a plurality of grids subject to contamination by trace impurities capable of undesired emission of electrons, and a final anode to be established at an operating potential substantially greater than at least one of the grids, the process including the steps of, establishing a ground plane on the outer surface of the tube neck, applying a high voltage age potential in increasing stages between the anode and the grid, and increasing the high voltage age potential for a predetermined interval during each stage to induce arcing within the tube.

2. The process of claim 1 wherein the high voltage age potential is increased in stages from ybetween 10,000 volts to 50,000 volts.

3. The process of claim 1 wherein the: increase in the high voltage age potential for a predetermined interval during each step to induce arcing is from. about 5,000 to 10,000 volts above the stage potential.

4. A process for reducing the tendency for arcing among the parts of a cathode ray tube having an electron gun structure which comprises a plurality of grids including a focus grid coupled to a reference potential and positioned intermediate lirst and second accelerating electrodes which are electrically connected to each other by a shield positioned about the focus grid and are operated at a potential substantially greater than the focus grid, and wherein the grids are subject tot contamination by trace impurities capable of undesired emission of electrons, the process including the steps of, getter flashing the tube, establishing a ground plane about the outer surface of the tube neck, applying a high voltage aging potential in increasing stages between the rst and second accelerating electrodes and the grids `of the electron gun assembly, and periodically boosting the high voltage age potential for a predetermined interval during each stage to foster arcing between the tube parts thereby ionizing the residual gasses within the tube to render the trace impurities ineffectual to cause arcing with the normal tube operating potential on the accelerating electrodes.

5. The process of claim 4 wherein the normal operating voltage on the iirst and second accelerating electrodes is on the order of 25,000 volts, and the high voltage age potential is increased in steps from between 15,000 to 40,000 volts.

6. The process of claim 5 wherein the booster voltage to induce arcing during each step is from 5,000 to 10,000 volts above the step potential.

7. Apparatus for reducing the tendency in a television receiver for arcing among the parts of a cathode ray tube having an electron gun structure positioned in the tube neck which includes a plurality of grids subject to contamination by trace impurities capable of undesired emission of electrons, and a final anode to be established at an operating potential greater than at least one of the grids, the apparatus including in combination, a high voltage source, timing means coupled to the voltage source for controlling the same to apply a predetermined voltage to the nal anode of the electron gun assembly for a predetermined time, means for connecting the plurality of grids of the electron gun assembly to a reference potential, and electrical conducting means encircling the tube neck and being connected to a reference potential, said conducting means developing electrical fields about the tube neck to simulate the environment surrounding the same during normal operation thereof in a television receiver.

8. The apparatus of claim 7 wherein the conducting means includes a grounded metal strap encircling the tube neck.

9. The apparatus of claim 7 in which the electron tube further includes a stem member supporting a plurality of connector pins, each of which is connected to a respective grid of the electron gun, and the apparatus further includes a container holding a plurality of metal bers, said container being positioned so that the connector pins extend into said container and contact said metal fibers thereby grounding the grids of the electron gun.

References Cited UNITED STATES PATENTS 3,323,854 6/1967 Palac 316-1 RICHARD H. EANES, JR., Primary Examiner.

U.S. Cl. X.R.

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